Recent developments and advances in information technologies have led to new and unanticipated problems. In particular, transfer of data from a server to a requesting client presents certain complication. For example, video data comprises a series of still frames which must be played one after another in a predefined and well regulated time sequence. Accordingly, information relating to the image data must be transferred along with information relating to the timing of playback events. Proper transmission of video images requires a scheme to preserve signal timing attributes from a transmitting station to a receiving station.
For proper play-back, an audio-video signal is preferably played out at the same rate which it is transmitted. This is especially important in interactive systems where “real-time” properties are maintained. If a receiver clock is independent from a transmitter clock then the receiver may play frames slightly faster than it receives them and lead the system into a data starvation condition. Alternatively, if the receiver plays frames too slowly, then a data overflow condition may occur at a data buffer having a limited size.
In certain transmission networks a data stream is divided into many portions or “packets” and transmitted along various paths of the network. These packets may be subject to time delays which are random in length. Sometimes and herein referred to as “jitter”, random time delays are necessarily inherent in networks which transmit data in data subsets. Each data packet may arrive at a receiver with a total transmission time which may vary from packet to packet. Depending upon the network path and network congestion conditions, transmission time delays may be highly different between packets. For audio-video data to be useful, it must be transmitted through the packet network and played back in a manner where the time delays or network jitter does not show up as artifacts in the presentation level play back. In order to achieve this, it is necessary that a time base of the transmitting station be replicated at the receiver and thus the “clocks” of the terminal end are said to be synchronized.